1. Field of the Invention
The present invention relates generally to connectors for use with tubing members, and specifically to connectors for use with coiled tubing strings of the type which are used to convey tools within a wellbore through the production tubing of the wellbore.
2. Description of the Prior Art
Recent advances in the technology relating to the work-over of producing oil and gas wells have greatly enhanced the efficiency and economy of work-over operations. Through the use of either a coiled-tubing string, or a wireline assembly, work-over operations can now be performed through the production tubing string of a flowing oil and gas well. Two extremely significant advantages have been obtained by the through-tubing technology advances. First, the production tubing string does not need to be removed from the oil and gas well in order to perform work-over operations. This is a significant economic advantage since work-over rigs are expensive, and the process of pulling a production tubing string is complicated and time consuming. The second advantage is that work-over operations can be performed without "killing" the well. The "killing" of a producing oil and gas well is a risky operation, and can irreparably damage the worked-over well. Until the recent advances in the through-tubing work-over technology, work-over operations usually required that the well be killed.
The through-tubing tools which are commercially viable at this time are predominantly fluid-pressure actuated, and most include an inflatable element which is run into the well in a radially-reduced position during a running mode of operation, and then selectively inflated into a radially-enlarged position during a setting mode of operation.
At present, these inflatable elements are commercially available in four sizes, with outer diameter dimensions ranging from 2.13 inches to 3.38 inches. It is thus possible to run these inflatable elements into wellbores through production tubing which is as small as 2.250 inches in inner diameter. Therefore, a through-tubing wellbore tool string may be expected to be passed through lengthy production tubing strings with less than 0.063 inches between the wellbore tool and the production tubing.
If the tubing-conveyed wellbore tool is unable to be passed through the entire length of the production tubing string, the significant benefits and advantages of using the through-tubing tool cannot be reaped. Furthermore, if the tubing-conveyed wellbore tool becomes stuck within the wellbore, either during running in or out of the well, many of the advantages of using tubing-conveyed, through-tubing wellbore tools disappear.
Different tool types have been designed, all using the inflatable element, to perform various work-over operations, including: permanent and temporary water shut-off of lower zones, zone abandonments, cement squeezing, gas shut-off of intermediate zones, acid and chemical treatments, selective acidizing, downhole flow modifications, fracturing isolation, and production testing operations. These tools typically include one or more fluid-actuated packing or plugging elements.
Tubing-conveyed wellbore tools require a secure connection to the lowermost end of the string of coiled tubing. Prior art tubing connectors operate by gripping the exterior of the tubing. These connectors include a fishing neck to facilitate fishing operations, should the connector fail to maintain a good connection with the tubing string and become separated from the tubing string. The fishing neck requires a structural profile. The prior art coupling between tubing string and wellbore tool also carries a seal to prevent leakage at the connection, and a gripping assembly to grip and hold the coiled tubing string. In order to meet all these objectives, the prior art tubing connector have a considerable thickness and thus extend into much of the clearance between the tubing string and the wellbore production tubing, increasing the risk of becoming stuck when running in or out of the wellbore.